Semiconductor light emitting diode (LED) is receiving attention from various fields as an environment friendly light source. Recently, as applications of LEDs are expanding to various fields such as interior and exterior illuminations, automobile headlights, and back-light units (BLU) of display devices, there are needs for high optical efficiency and excellent heat radiation characteristics. For high efficiency LEDs, materials or structures of the LEDs should be improved primarily, however there is a need for improvement in the structures of the LED packages and the materials used therein.
That is, in a high efficiency LED, high temperature heat is produced, therefore this heat must be radiated effectively otherwise temperature rising on the LEDs causes ageing of the characteristics thereby shortening the lifetime. In high efficiency LED packages, efforts on effective radiation of the heat produced by the LEDs are making progress.
FIG. 1 is an exemplary illustration of a cross-sectional view of an optical device wherein an optical device chip 40 is mounted inside the cavity 60 of a metal substrate 10 having a vertical insulation layer 20 formed therein.
Referring to FIG. 1, the metal substrate 10 having a vertical insulation layer 20 formed therein can be formed, for example, by vertically cutting a stack into pieces having a predetermined length (width), wherein said stack is formed by alternately stacking (or forming) metal substrates and insulation layers. Aluminum, copper, or an alloy comprising at least one of foresaid materials and the like having a good thermal conductivity and electrical conductivity, may be used as a material for the metal substrate 10 having such a vertical insulation layer 20 formed therein. Further, a cavity 60, having a downwardly narrowing taper formed by machining or chemical etching and the like, is formed on the upper surface of the metal substrate 10 having a vertical insulation layer 20 formed therein.
Meanwhile, in order to enhance the reflection property of the light generated from the optical device chip 40, or the bonding property, for example, a silver-plated layer 30 is formed on the main wall of the cavity 60 and on the upper surface of the metal substrate 10 using a metal plating process such as an electroplating process, an electroless plating process, or a sputtering process. An optical device chip 40 is bonded on a portion of the upper surface of the silver-plated layer 30 inside the cavity 60 using a silver epoxy adhesive.
For an optical device having an above described structure, a silver epoxy has a good electrical conductivity and bonding property, however, the relatively low heat conductivity thereof generates a thermal resistance in a package wherein a high power optical device is mounted. Thereby, the overall heat radiation property of the package is degraded so that the life of the optical device chip 40 is eventually shortened. Moreover, the foresaid problem will be more significant if the optical device chip 40 is an UV optical device which generates more heat compared to an optical device for a visible light region.